The present invention relates to a clamping device for injection-molding machine, and more particularly to a clamping device for injection-molding machine including a high-speed screw rod unit, a lead of which can be changed to enable closing of mold at a high speed and producing of a high-pressure clamping force for closing mold.
The clamping device is one of many critical parts in an injection-molding machine to ensure reliable closing of mold. Since molten material is supplied into a mold cavity under a extremely high pressure, it is necessary to apply a sufficient clamping force to tightly close the mold to avoid flashing, molded products with flashes, or other conditions that would adversely affect the quality of the molded products.
In closing the mold, it is desirable the clamping device is moved at a high speed to save time, and provides a sufficient clamping force at the time two mold halves of the mold contact with each other in order to tightly close the mold.
FIG. 1 shows a conventional power-driven clamping device, in which a servomotor 1 is employed to rotate a timing belt pulley 2. A dynamic force produced by the servomotor 1 is transmitted to a nut element 4 via the timing belt pulley 2 and a timing belt 3 wound around the timing belt pulley 2, so that the nut element 4 is driven to rotate a screw rod 5. A rotating motion of the screw rod 5 is converted into a linear motion, enabling the screw rod 5 to move reciprocatingly. By rotating the servomotor 1 forward or reversely, a movable mold 6 connected to the screw rod 5 is closed to or moved away from a fixed mold, respectively.
To enable movement of the movable mold 6 at a high speed, the above-described conventional clamping device has to employ a screw rod having a relatively large lead to increase the moving speed of the mold 6. However, when the servomotor 1 has a fixed power, the screw rod 5 with a large lead has a large pitch and accordingly an acting force with a small rate of amplification. This condition prevents the conventional clamping device from producing a large clamping force during closing mold. Due to the small clamping force, many problems, such as flashing, molded products with flashes or inferior quality, etc., would occur.
On the contrary, when a screw rod with a small lead is employed in the clamping device, the acting force thereof would have a relatively large rate of amplification. However, the screw rod would take more time to complete the closing of mold. That is, the time for the clamping device to complete one molding cycle is extended and the productivity of the injection-molding machine is reduced to increase the overall manufacturing cost of the molded products.
If it is desired for the conventional clamping device to close the mold at high speed and under high-pressure clamping force, it is necessary to increase the power of the servomotor, so as to supply an increased dynamic force. However, a high-power servomotor consumes extremely high power and has a big volume to result in waste of energy, increased equipment cost, and occupation of large space.
It is therefore an important and critical issue to develop a power-driven clamping device for injection molding machine that enables closing of mold at high speed and under high-pressure clamping force with a low-power driving source.